There are numerous applications for monomolecular layers or films of organic compounds, particularly in electronics, where they are used for example for forming metal-insulator-metal structures, in which the thickness of the dielectric layer is particularly carefully controlled.
A known method for producing and depositing monomolecular layers of amphiphilic molecules has been described by Langmuir. According to this method, a solution of amphiphilic molecules dissolved in a solvent which is imiscible with the liquid of the tank is placed on the surface of said liquid. For example, the solvent is chloroform or petroleum ether. The solvent evaporates, leaving behind the molecules partly immersed in the water with their major axis oriented in a random manner. The molecules are straightened by compression using a barrier providing a given surface pressure. The thus formed film can be deposited on a hydrophilic or hydrophobic substrate. Hydrophilic substrates are, for example, oxides such as Al.sub.2 O.sub.3, CaF.sub.2 and SiO.sub.2. Hydrophobic substrates are pure metals such as gold, silver or germanium. The monomolecular film is deposited on the surface of the substrate previously immersed in the liquid of the tank by slowly raising the former, whilst maintaining the film at said given surface pressure throughout the duration of the deposition. Use is made of a liquid tight barrier, which is mobile on the surface of the tank liquid for carrying out the compression of the monomolecular film. As a result of the displacement of this barrier, there is a reduction of the area of the monomolecular film previously formed on the surface of the liquid, so as to bring it to the desired surface pressure.
Throughout the operations of producing and depositing the film, absolute cleanness is required, together with the absence of pollution of both the bath and its surface by complexing or surfactant ionic products.
The prior art discloses a large number of tanks permitting the formation and deposition of monomolecular layers or films according to the Langmuir method. For example, the Joyce-Loebel company (Team Valley, Gateshead, G.B.) markets a glass tank with a constant perimeter Teflon tape barrier. The Lauda Company (German Federal Republic) markets a sheet metal tank covered with Teflon, which is of a small size and has a Langmuir balance. Finally, Rev. Sci. Instrum., vol. 46, no. 10 Oct. 75, Peter Fromhertz describes a small circular tank. However, these devices require a high degree of skill for use and suffer from serious cleaning and pollution problems.
Thus, in the case of the tank marketed by Lauda, the mobile barrier is constituted by a strip placed on the rim of the tank. Thus, the latter must contain a very precise liquid quantity and if the quantity is excessive, the tank overflows. If the quantity is inadequate, the meniscus is not formed.
In the case of the tank marketed by Joyce-Loebel, the mobile barrier is constituted by a constant perimeter tape. This system suffers from two disadvantages. Firstly the mechanism has rotary pulleys passing through the surface in the compartment of the film, which shears the fragile monomolecular film and deposits it on the pulleys and on the tape. In addition, said device has areas which cannot undergo surface cleaning, inter alia the area of the tank outside the tape, where the film formed by the impurities from the water cannot be compressed in order to be collected and subject to suction action.